Generally described, turbo-machinery, such as gas turbine engines and the like, includes a main gas flow path therethrough. The main gas flow path generally includes a gas intake, a compressor, a combustor, a turbine, and a gas outlet. Gas leakage, both out of the gas flow path or into the gas flow path, may be detrimental to overall engine performance and is generally otherwise undesirable. Gas path leakage may lower the efficiency of the gas turbine engine, increase fuel costs, and possibly increase emission levels.
Secondary gas flows may be used within the gas turbine engine to cool the various heated components. Specifically, cooling air extracted from the later stages of the compressor in a gas turbine engine may be used for cooling the components therein and for purging gaps and cavities between adjacent components. Cloth seals may be mounted in slots between the adjacent components so as to control the amount of the secondary flow extracted by metering its leakage into the hot gas path. Cloth seals hence are widely used to control the amount of cooling and purge air required to prevent hot gas ingestion and overheating of turbine parts such as shrouds, nozzles, and the like. Cloth seals thus may seal the gaps between adjacent turbine parts (shroud/shroud, shroud/nozzle, etc.) that are needed to accommodate typical thermal and mechanical transients during turbine engine operation. Cloth seals provide the dual advantage of effectively sealing these gaps while also providing good wear resistance due to the presence of the sacrificial cloth layers.
Reducing the leakage through the cloth seals themselves thus may reduce the amount of the secondary flow extracted from the compressor stages. Likewise, the reduced leakage through the cloth seals may result in improved overall thermal efficiency and power output from the turbine. Leakage across a cloth seal generally may be found in two areas:
(1) leakage from under a metallic shim that runs the length of the cloth seal; and
(2) leakage through a gap between the ends of the cloth seal and the ends of the mating slot.
The latter part may be dominate in typical cloth seals and may contribute as much as seventy-five percent (75%) of the total leakage therethrough. Reducing the end gap may not be feasible due to assembly considerations, tolerance stack up, and the need to accommodate possible relative motion between the adjacent components. A portion of the end gap leakage may travel through the clearance gap between the two turbine components, while a majority of the leakage may extend through the porous bottom cloth layer along the seal length and eventually leak through the clearance gap. This leakage through the porous bottom cloth layer may contribute to about half of the total leakage therethrough.
There is thus a desire for improved cloth seal design. Such an improved design may limit end gap leakage, particularly through the porous bottom cloth layer. Reducing the leakage therethrough may improve the overall efficiency and power output of the gas turbine engine as a whole.